Technical Field
This invention relates to GNSS surveying, and more particularly to a mobile base station and data collector with electronic leveling to facilitate automated data capture.
Background Information
The USGS (U.S. Geological Survey) Global Navigation Satellite System (GNSS) is a system of satellites that provide autonomous geo-spatial positioning with global coverage. It allows small electronic receivers to determine their location (longitude, latitude, and altitude) to high precision using time signals transmitted along a line of sight by radio from satellites. GNSS is commonly used for various navigation and surveying functions.
Differential grade GNSS equipment differ from commercial grade GPS units by incorporating higher quality antennas and implementing differential corrections that greatly improve the accuracy of the location determination. Differential grade GNSS equipment incorporating high quality antennas can receive information from a greater number of satellites at once, some can receive information from the satellites in several frequencies (L1 and L2), and some can receive information from satellites in different satellite systems (primarily GPS and GLONASS). Differential grade antennas receive corrections from either a satellite based augmentation system (SBAS) or ground based augmentation systems (GBAS). The accuracy of the SBAS and the GBAS corrections depends on the type of system being used and the user's location in relationship to the system's coverage. In addition, differential grade units typically have higher quality mapping software designed to map features using points, lines, and polygons.
As mentioned, a significant aspect of differential-grade GNSS systems is their ability to apply differential corrections to positions. There are several different ways to apply these corrections. One method is to post-process the data after it is collected with data from a nearby base station, however, real time corrections, e.g., using an RTK (Real Time Kinetic) base station, are more commonly used. The types of real-time corrections that can be used depend upon the particular device being used.
Accuracy of differential-grade GNSS units varies depending upon the type of differential correction applied and the quality of the GNSS receiver and antenna (type, quality, and the number of satellite and frequencies that can be received), with external antennas typically providing the best results.
Survey Grade GNSS Equipment
Survey-grade GNSS receivers typically record the full-wavelength carrier phase and signal strength of the L1 and L2 frequencies and track at least eight satellites simultaneously on parallel channels. The antennas used for GNSS survey applications should have stable phase centers and be designed to minimize multipath interference. Survey grade GNSS equipment also include fixed-height, accurately leveled tripods 10 and roving range poles 12, e.g., for RTK procedures, such as shown in FIG. 1.
Real-Time Kinematic (RTK) Procedures
Kinematic is a term applied to GPS surveying methods where receivers are in continuous motion, although for relative positioning the more typical arrangement is a stop and go technique. As shown in FIG. 1, this approach involves using at least one stationary reference receiver/tripod 10 and at least one moving receiver called a rover or roving range pole/receiver 12. RTK procedures do not require post-processing of the data to obtain a position solution. Rather, a radio at the reference receiver 10 broadcasts the position of the reference position to the roving receivers 12. This allows for real-time surveying in the field and allows the surveyor to check the quality of the measurements without having to process the data. It is noted that conventional approaches require both the reference receiver/tripod 10 and the roving pole 12 to be properly leveled during data capture in order to provide desired accuracy. This leveling is conventionally provided by the use of conventional bubble levels mounted on the poles of devices 10, 12. This conventional leveling approach generally suffices for the tripod 10 due to its stationary use. However, this approach tends to be cumbersome for the rover 12, because it generally requires the user to stop, observe the bubble level on the pole in order to move the pole to proper vertical orientation, and then hold the pole in position while looking away from the pole to a data collector to capture the data. This leveling process is repeated at each data collection location throughout the work site.
A need exists for an improved system and method to facilitate leveling of RTK rovers and related GNSS equipment and/or to otherwise improve RTK data collection.